1. Field of the Invention
The present invention relates to a process for improving the processing parameters and the mechanical properties of mixtures based on hydraulic binders, especially Portland cements or similar cements. The invention also relates to novel compositions which can be used as adjuvants in mixtures based on hydraulic binders.
2. Description of the Prior Art
It is well known to this art that a mixture consisting of hydraulic cement, of water and of a filler such as sand or gravel [hereafter referred to as a hydraulic cement composition] gradually loses its fluidity once the mixture has been prepared, due to the progress of setting, and in the case of concrete this loss is referred to as the loss of ability to flow and spread. Thus, if a long time is provided between mixing the cement and casting same, it is necessary to prevent this loss in fluidity.
In order to restore fluidity to the cement if the cement composition has become viscous, the addition of water has hitherto been employed. However, in such a process, the weight ratio of mixing water/cement [hereafter referred to as the W/C ratio] is altered (increased) by the addition of water, and this results in undesirable phenomena, such as a reduction in the mechanical strength of the finished product.
In order to overcome the above-mentioned disadvantages, it has been proposed to add to the hydraulic cement compositions dispersing agents which function to bring the binder into a fluid and easy-to-work form, while tending to reduce the amount of water necessary for mixing; these agents are commonly referred to as water-reducing agents.
The prior art, especially U.S. Pat. Nos. 2,141,569, 3,277,162 and 3,677,780 and French Patent No. 2,165,681 teaches that from among the water-reducing agents, the best known and also the most commonly used are the water-soluble arylsulfonate or alkylarylsulfonate salts, the organic moiety of which either may or may not have been condensed with formaldehyde. However, these products are still not completely satisfactory because their use in cold weather, especially at temperatures of between 0.degree. and 15.degree. C., is accompanied by a slowing down of the hardening. If such dispersing agents are added to cements, good results are indeed observed in respect to fluidity, but, on the other hand, it is found that the initial mechanical strengths, for example, those measured after 24 hours, are substantially reduced. Accordingly, a serious need exists in this art for a process to improve the properties of hydraulic cement compositions which makes it possible to overcome the noted disadvantage of lowering of mechanical strengths as a result of cold weather, while at the same time preserving the above-mentioned advantages, in particular the fact that a fluid, easy-to-work binder is obtained.